X-ray diffraction apparatus



Original Filed Sept. 11, 1956 INVENTORI- LLOYD R. ROSE BY.-

ATTORNEY fitates The present invention relates in general to X-raydiifraction analysis, and has more particular reference to improvedspectrometric apparatus for the analysis of secondary or so-calledfluorescent X-rays emitted by an examination specimen when excited bythe impingement of primary X-rays thereon, the same comprising subjectmatter divided from the copending application for U.S. Letters Patent onthe invention of Lloyd R. Rose in X-ray Diffraction Apparatus, SerialNo. 609,175, filed September 11, 1956, now US. Patent 2,898,459, issuedAug. 4, 1959.

Any crystalline body may be constituted as a source of fluorescent orsecondary radiation in response to the application thereto of anexciting beam of primary rays or charged particles. Such inducedradiation is characteristic of the atomic composition of the material ofthe irradiated specimen, since the same comprises rays havingwavelengths and intensity ratios which are characteristic of theirradiated material and the nature of the radiation source. Thefluorescent radiation thus emitted by a crystal specimen, when suitablyexcited by application thereto of a primary X-ray beam, may be detectedin the form of an X-ray spectrum as a means for identifying or analyzingthe material of the specimen.

As stated in United States Letters Patent No. 2,540,821, which issuedFebruary 6, 1951, on the invention of David Harker in X-rayspectrometer, it has heretofore been suggested that the apparentintensity of fluorescent specimen emitted X-rays may be increased by useof a bent crystal in obtaining the diffraction spectrum. Such use of abent crystal, however, involves either the provision of means foraltering the curvature of the bent crystal as the detector is moved toscan the resulting spectrum, or the provision of means for altering thespacement between the crystal and the detector during spectrum scanningmovement of the detector, in order to keep the diffracted spectrumforming rays focused upon the detector.

An important object of the present invention is to pro vide fixed focusapparatus for supporting an X-ray detector in position to scan an X-rayspectrum produced by a bent diffraction crystal of fixed configuration,the mechanism serving to maintain the crystal and the detector at alltimes in an appropriate fixed focus relation with re spect to astationary examination specimen, while permitting the crystal anddetector to be adjustably shifted with respect to the stationaryspecimen in fashion causing the detector to traverse and hence scan thespectrum.

Another object of the invention is to provide spectrometric apparatus ofunusual simplicity for the accomplishment of crystal analysis; a furtherobject being to provide apparatus of rugged character, rapidly operablein analyzing th X-ray spectrum of an examination specimen.

Another important object is to provide turnable mechanism for adjustingthe angularity of a bent crystal with respect to a stationaryexamination specimen and simultaneously adjusting a scanning detectorwith respect to the crystal to maintain the detector at all times in thepath of crystal diffracted rays applied thereto from said stationaryspecimen.

Another important object is to provide an adjustable frameworkcomprising relatively pivoted links operatively associated with a fixedspecimen mounting station and ire serving to shiftably support adiifraction element comprising a bent crystal and an X-ray spectrumdetector, in order to maintain the detector in position with respect tothe crystal to receive the impingement of diffraction X- rays directedupon the crystal as the result of X-ray excitation of the examinationspecimen.

Another important object is to provide gear means for determining therelative angular position and spacement between the crystal, thedetector and the specimen station.

Briefly stated, the invention provides an adjustable supportingframework having a fixed station for receiving an examination specimen,and support members shiftably and turnably mounted with respect to thespecimen support station in order to support a detector adjustably inspaced relation with respect to the specimen station, and also tosupport a bent diffraction crystal at all times and for all adjustedpositions of the detector at such an angle with respect to the detectorand station as to apply a diffraction spectrum upon the detector inresponse to the application of fluorescent rays emitted by a specimen atsuch station and applied upon the diffraction crystal as the result ofX-ray excitation of the specimen at the station.

The foregoing and numerous other important objects, advantages, andinherent functions of the invention will become apparent as the same ismore fully understood from the following description, which, taken inconnection with the accompanying drawings, discloses preferredembodiments of the invention.

Referring to the drawings,

The single FIGURE is a diagrammatic view of adjustable mechanismproviding a bent crystal focusing system embodying the invention.

. To illustrate the invention the drawings show X-ray spectographicapparatus embodying a main frame carrying an X-ray source 11, such as aconventional X-ray generating tube, and an examination specimen 13 ofcrystalline material to be analyzed, said specimen being supported at afixed examination station on the main frame in the path of a beam ofprimary X-rays 15 emitted by the source 11. Application of the X-raybeam 15 upon the specimen 13 Will excite the same for the emission ofsecondary or fluorescent X-rays therefrom, which secondary rays arecharacteristic of the atomic composition of the specimen. Some of suchX-rays may be emitted in a direction to pass through a slit-like opening17 formed in a pane or panel 19 of material that it rela-' tivelyimpervious to X-rays, said opening 17 thus comprising a stationarysource slit defining a beam 21 emitted by the specimen 13 and comprisingfluorescent X-rays characteristic of the material of the specimen.

The apparatus of the present invention also embodies a diffractioncrystal 23 turnably supported in the path of the beam 21, said crystalserving to diffract the ray beam in known fashion and focus thediffracted beam upon a ray sensitive detector 25, the diffracted beambeing delivered through a slit-like opening 27 formed in a plate 29 ofmaterial that is relatively opaque to X-rays.

In order to analyze the X-ray spectrum of the diffracted beam, thepresent" invention provides adjustable mechanism 31 operable toprogressively alter the inclination at which the ray beam 21 impingesupon the diifraction crystal 23 and the corresponding angularity of thedetector 25 in position with respect to the crystal to receive thefocused impingement of the diffracted beam on said detector. Themechanism 31 is supported on the main frame and is arranged so that thediffraction crystal 23 is at all times in alined position to receive theimpingement of the ray beam 21, the examination sample 13 and the X-raysource 11 at all times remaining fixed on the main frame. The mechanism31 is also arranged so that the configuration of the diffraction crystal23 remains fixed.

The mechanism 31 may comprise a fixed gear segment 55 subtending anangle somewhat in excess of 90 and secured on the main support frame inposition such that the gear segment is centered on an axis in alinementwith the beam defining slit 17 in the plate 19. The mechanism 31 mayalso comprise a support arm 57 pivotally supported at one end forturning movement about an axis in alinement with the beam defining slit17, the opposite end of said arm 57 extending to and providing a pivotaxis 59 which at all times lies at the center of a focusing circle 51.It will be noted that, in each position of adjustment of the mechanism31, the diffracting surface of the crystal 23 and the beam guiding slits17 and 27 lie on the focusing circle 51 which is of uniform size for alladjusted positions of the mechanism 31. The diffraction crystal 23 issupported upon one end of a carrying arm 61, the opposite end of whichis pivotally mounted upon the support arm 57 at the axis 59.

A detector supporting arm 63 is also supported at one end on the arm 57for pivotal movement about the axis 59, the other end of said supportarm 63 carrying a gear Wheel 65 turnably mounted thereon for rotationabout an axis 67 which is at all times disposed upon the focusing circle51. The detector 25 is supportingly secured on the gear wheel 65, whichalso carries the plate 29 in' which the slit 27 is formed in alinementwith the pivot axis 67. The carrying arms 61 and 63 and the support arm57 are drivingly interconnected by means of bisecting gears including agear 69 having teeth meshing with the teeth of the segment 55, the teethof said gear 69 also being drivingly interconnected with the teeth of agear 71, which is fixedly connected with the detector carrying arm 63and mounted for turning movement on the support arm 57 about the axis59. Fixed to and driven with the gear 69 is a spur gear 7-3 having teethdrivingly meshed with the teeth of a gear 75, which is fixedly connectedwith the crystal carrying arm 61 and supported on the arm 57 for turningmovement about the axis 59. The driving ratio of the gears 73 and 75 maybe double that of the gears 69 and 71 so as to maintain the crystal 2.3at all times in position on the focusing circle midway between the slits17 and 27, the gears 69, 71, 73 and 75 thus functioning as bisectinggears.

The arm 63 may also carry a gear 77 turnably mounted thereon in positionto drivingly engage the detector carrying gear 65 and the gear 75 whichfunctions to turn the crystal carrying arm 61 about the pivot axis 59.The gears 65, 75 and 77 are so proportioned as to adjust'the detectorcarrying gear 65 in position at all times to aim the detector and theslit at the diffraction crystal. If desired, the main frame may beprovided with a cam slot defining the path of the axis of the detectorcarrying gear 65.

It will be seen from the foregoing that the diffraction angle may bedetermined as one-half of the angle made between the carrying arm 61 andeither of the arms 57 and 63 at the axis -9, the same being one-quarterof the angle defined between the arms 57 and 63. The diffraction angle,accordingly, maybe measured on a suitable graduated protractor appliedto the arms. It will be seen also that the diffraction angle is'afunction of the angularity of the carrying arm 57 about its mountingaxis on the main frame. The ditfraction angle, therefore, may

' be determined by means of a graduated protractor dis posed in positionto determine the relative angularity of the arm 57 with respect to themain frame. It will be apparent, also, that the diffraction angle is afunction of the relatively turned positions of any of the gears and maytherefore be revealed upon any suitable or preferred indicator meansdriven by or in unison .with the movement of any of the gearsfid, 69,7-1,,73, 75 or 77. Any suitable or preferred manually operable or motordriven means any, of course, be provided for turning the gears for thepurpose of adjusting the mechanism.

The foregoing fixed focus spectrometric mechanism is particularly usefulsince adjustment thereof in diffraction analysis requires no motion ofthe X-ray tube, the sample and the source slit. As a consequence, themechanism may be employed in analyzinghorizontally supported samples,including liquid bodies. The mechanism furthermore is of simple,uncomplicated character in that the diffraction crystal has fixedconfiguration, thereby avoiding the necessity of providing mechanism foradjusting the shape of the crystal during movement of the mechanismduring diffraction analysis.

It is thought that the invention and its numerous attendant advantageswill be fuily understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts without departing from the spirit orscope of the invention, or sacrificing any of its attendant advantages,the forms herein disclosed being preferred embodiments for the purposeof illustrating the invention.

The invention is hereby claimed as follows:

1. Diffraction apparatus comprising: a specimen support; an apertureddevice fixedly positioned relative to said support; a diffractioncrystal; a ray sensitive detector; said apertured device, crystal anddetector being positioned relative to each other to define a circlehaving a predetermined radius; and means comprising a plurality ofconnected gears for moving said crystal and said detector relative toeach other and moving each both rotationally and translationallyrelative to said apertured device to change the position of the centerof said circle while maintaining its radius constant.

2. Diffraction apparatus as recited in claim 1 wherein said meansincludesmeans constraining the translational motion of the axis of saiddiffraction crystal along a single imaginary line passing through theaperture of said apertured device.

3. Diffraction apparatus as recited in claim 2 including means to rotatesaid crystal about its axis by an amount uniquely determined by thedistance of said crystal from said aperture whereby a ray passingthrough said aperture illuminates a constant area of said crystalirrespective of the distance between said crystal and said aperture.

4. X-ray diffraction apparatus comprising: a source of X-rays; aspecimen support disposed in the path of said X-rays and in fixedangular relation thereto, the relation of said source and supportthereby defining a second X-ray path from said specimen fixedly orientedspace; an X-ray diffraction crystal mounted in said sec- 0nd path; anX-ray sensitive detector positioned to view X-rays from said diffractioncrystal; and motive means connected to said crystal and said detectorfor simultaneously moving said crystal linearly along said second X-raypath exclusively and said detector along a path to maintain said view ofsaid crystal, and for rotating said' an examination station in positionfor irradiation with penetrating rays, :1 source collimator formed witha slit for defining a beam of secondary radiation emitted from aspecimen irradiated at said station, a diffraction crystal,

a first movable arm carrying said crystal at an end therea of, a secondmovable arm supported at one end on said frame or. base for pivotalmovement about an axis in alinement with the slit of said sourcecollimator, a detector and an associated collimator forming a slitadjacent the detector, 2. third. movable arm carrying said detector andassociated collimator for turning movement on an end of said third armabout an axis in alinementwiththe slit of said detector associatedcollimator, the

other end of said third arm and the crystal remote end of said first armbeing supported for pivotal movement about a common axis at thecollimator remote end of said second arm, and gear means for turning thesecond arm on said frame, for turning said first arm carrying saidcrystal and said third arm carrying said detector with respect to thesecond movable arm, and for turning the detector and associatedcollimator with respect to said third movable arm.

6. Diffraction apparatus as set forth in claim 5, wherein the gear meansturns the first arm on the second movable arm at twice the angular rateat which the third arm carrying said detector is turned.

7. Diffraction apparatus as set forth in claim 5, wherein the gear meansturns the detector on the third arm at an angular rate to maintain thedetector and associated collimator slit at all times aimed precisely atthe crystal.

References Cited in the file of this patent UNITED STATES PATENTS2,648,011 Good Aug. 4, 1953 2,783,385 Wytzes Feb. 26, 1957 2,805,341Lang Sept. 3, 1957 2,898,470 Khol Aug. 4, 1959 2,901,629 Friedman Aug.25, 1959 2,924,715 Hendee et al. Feb. 9, 1960 3,005,098 Buschmann Oct.17, 1961

1. DIFFRACTION APPARATUS COMPRISING: A SPECIMEN SUPPORT; AN APERTUREDDEVICE FIXEDLY POSITIONED RELATIVE TO SAID SUPPORT; A DIFFRACTIONCRYSTAL; A RAY SENSITIVE DETECTOR; SAID APERTURED DEVICE, CRYSTAL ANDDETECTOR BEING POSITIONED RELATIVE TO EACH OTHER TO DEFINE A CIRCLEHAVING A PREDETERMINED RADIUS; AND MEANS COMPRISING A PLURALITY OFCONNECTED GEARS FOR MOVING SAID CRYSTAL AND SAID DETECTOR RELATIVE TOEACH OTHER AND MOVING EACH BOTH ROTATIONALLY AND TRANSLATIONALLYRELATIVE TO SAID APERTURED DEVICE TO CHANGE THE POSITION OF THE CENTEROF SAID CIRCLE WHILE MAINTAINING ITS RADIUS CONSTANT.